1. Technical Field
The present invention relates to a wireless power transmission apparatus and method.
2. Description of the Related Art
With the development of wireless communication technology, ubiquitous information environments enabling anyone to exchange desired information anytime and anywhere have been implemented. However, most communication information devices still depend on batteries and are supplied with power by a wired power cord, and thus the use of communication information devices is limited. Therefore, the environment of a wireless information network cannot be actually freed from this limitation until the problem of terminal power is solved.
In order to solve this problem, various types of technologies for transmitting power in a wireless manner have been developed.
First, representative technologies may include radio reception technology using microwaves, magnetic induction technology using magnetic fields, and magnetic resonance technology using the energy conversion of magnetic fields and electric fields.
In this case, radio reception technology is advantageous because microwaves are radiated into the air through an antenna, and thus long-distance power transmission is made possible. However, radio reception technology has high radiation loss due to the consumption of power by the air, and thus the efficiency of power transmission is limited.
Further, magnetic induction technology is a technology based on the coupling of magnetic energy using the primary coil of a transmitting end and the secondary coil of a receiving end, and is advantageous in that the efficiency of power transmission is high. However, magnetic induction technology is disadvantageous in that the primary coil of the transmitting end and the secondary coil of the receiving end must be located adjacent to each other within a short distance of about several mm so as to transmit power. Furthermore, magnetic induction technology is disadvantageous in that the efficiency of power transmission rapidly changes according to the alignment of the primary coil of the transmitting end and the secondary coil of the receiving end, and in that the amount of heat generated is large.
Therefore, magnetic resonance technology that is similar to magnetic induction technology has recently been developed, but it is configured to concentrate energy on a specific resonant frequency determined by a coil inductor L and a capacitor C, and thus to transmit power in the form of magnetic energy.
Such a magnetic resonance technology is advantageous because a relatively large amount of power can be transmitted even a distance of several meters, but requires high resonance characteristics (high quality factor).
In other words, magnetic resonance technology is disadvantageous because the efficiency of power transmission rapidly changes depending on whether impedance matching has been realized or whether the resonant frequencies of the LC circuit of the transmitting end and the LC circuit of the receiving end are identical to each other.
In particular, impedance mismatching and transmission efficiency at low output power, which are caused by variations in the distance between the transmitting end and the receiving end, become principal factors which interfere with optimal wireless power transmission in wireless power transmission.
For this, conventional magnetic induction technology deals with the above problems via communication between the transmitting end and the receiving end by mounting communication devices (for example, transceivers) both on the transmitting end and on the receiving end.
However, when the communication devices (for example, transceivers) are separately mounted, problems arise in that costs required for a wireless power transmission apparatus increase, and the construction of the apparatus becomes complicated.
Further, a power amplifier for amplifying the output power to improve transmission efficiency at low output power must always be kept turned on even when power amplification is not required, and thus this driving of the power amplifier wastes power unnecessarily.